1. Field of the Invention
This invention pertains to mobile storage systems, and more particularly to apparatus for controlling the movement of mobile carriages.
2. Description of the Prior Art
It is well known to combine storage shelves with carriages that move along floor mounted rails. Such mobile storage units enable large quantities of materials to be stored in relatively small spaces while still providing easy access to all the stored items. Consequently, mobile storage systems that employ several mobile carriages are in widespread use in offices and libraries.
A mobile carriage and its load of books, papers, and other items may weigh several hundred pounds. Consequently, an electric power drive or a manual drive having a large mechanical advantage is usually employed to move the carriage along the rails without excessive human effort. Manually powered mobile storage systems normally include a handwheel located at one end of each carriage. The handwheel is typically linked to a chain and sprocket mechanism that connects with drive wheels in contact with the rails. By rotating the handwheel, the chain and sprocket mechanism operates to move the carriage along the rails independently of the other carriages in the system. Accordingly, aisles are created or dissipated between two adjacent carriages by causing the carriages to move toward or away from each other. When two adjacent carriages are separated from each other, a person can walk in the aisle between them to gain access to the materials stored within either carriage.
For safety purposes, it is desirable that the carriages not be movable when a person is standing in the aisle between them. For that reason, various types of locking devices have been developed to selectively prevent carriage movement along the rails. One type of prior lock employs pins that are actuable to enter between and withdraw from adjacent links of a chain of the chain and sprocket mechanism, The pins are housed in blocks fixed to the carriage frame such that engaging a chain with the pins prevents chain travel and thus carriage movement. A somewhat similar prior locking device uses two clamps that engage and disengage selected chain lengths between them. The clamps are mounted to the carriage frame, so carriage movement is prevented when the clamps engage the chain.
Although the prior locking devices are generally satisfactory, they nevertheless are subject to improvement.